Vacuum tube life meter



1934 L. A. GEBHARD ET AL VACUUM TUBE LIFE METER Filed Feb. 17, 1932 fl/I ATTORNEY Patented Nov. 27, 1934 1,981,860 I VACUUM TUBE LIFE METERLouis A. Gebhard and George E. Jacobson,

Washington, D. 0.

Application February 17, 1932, Serial No. 593,598 4 Claims. (01. 161-15) (Granted under the act of March 3, 1883, as amended April 30, 1928;370 0. G. 757) Our invention relates broadly to apparatus for use inelectron tube circuits and more particularly to a circuit arrangementand construction for determining the life and hours of service ofelectron tubes;

One of the objects of our invention is .to provide means for checkingthe operation of electron tubes for determining the total number ofhours of service an electron tube has given and to determine the numberof hours over which the circuit containing the electron tube has beenoperated.

Another object of our invention is to provide a compact construction ofmeter which measures the time period over which an electron tube hasbeen in use in order to warn the attendant with respect to the probablelife of the tube and to provide a check upon the manufacturer withrespect to the guaranteed life of the tube.

Still another object of our invention is to provide a construction oftime actuated device of measuring electron tube circuits for accuratelychecking the performance of the electron tube while offering nointerference to the normal operation of the circuits in which theelectron tube under inspection is being operated.

A still further object of our invention is to provide a construction ofelectron tube life meter which is particularly adapted for electron tubecircuits employing tubes having their cathodes energized fromtransformers having a grounded center tap-secondary winding, wherein thelife of the tube may be determined without interfering with the normaloperation of the transformer system.

Other andfurther objects of our invention reside in the construction ofan electron tube life meter as set forth more fully in the specificationhereinafter following by reference to the accompanying drawing, wherein:

Figure 1 diagrammatically illustrates the circuit arrangement for theelectron tube life meter of our invention; Fig. 2 is a front view of theelectron tube life meter; Fig. 3 is a top view 'of the electron tubelife meter; Fig. 4 is a bottom view of the electron tube life meter;Fig. 5 is an enlarged view of the transmission shaft showing the mannerof insulating the shaft for the protection of the power supply circuitsleading to the cathode of the electron tube under measurement; and Fig.6 is a cross-sectional view of the insulation means surrounding thedrive shaft which leads to the counter in the electron tube life meterof our invention.

Where vacuum tubes are purchased on a guaranteed life basis it isdesirable, and in fact necessary, to know the total number of hours ofservice the tube has given. Where tubes are not purchased on this basisit is desirable to know just how much life the tube has had so as tocheck up 80 on its performance. It is also desirable to know just howmany hours a particular radio transmitter has been operated. Thisinformation may be obtained by use of the device of our invention whichwe have termed an electron tube life meter.

The meter shown in Fig. 1 consists of an electrically operated clock 1which is connected to a counting mechanism 2 by means of a flexibleshaft 3. The counting mechanism 2 is supoprted by insulated yoke. 4.frominsulated panel 5. Insu- 7 lated panel 5 also supports the clock 1 bymeans of screws 6 and 7 which pass through ring member 1a which abutsagainst lugs lb projecting from the casing 1 of the electric clock. Theelectric clock is shown having a setting device 21 projecting fromcasing 1. Terminal 22 is grounded direct to the casing of the clockwhile the terminal 23 is insulatingly mounted on casing 1. Screws 8 and9 fasten the mechanism to any desired surface, such as the panel 10 ofthe transmitting apparatus. The counting mechanism 2 is so arranged thatone .turn of its shaft 11 will cause one number to be counted by itsdial 12. The mechanism is so arranged that the dial 12 is visiblethrough the aperture '16 in the front panel 86 of the radio transmitteror can be seen by opening a door in the front of the panel. The flexibleshaft 3 consists of a spring which is shown in detail in Fig. 5. Thisflexible shaft 3 is con nected through a sleeve 17 to the shaft 18 which90 carries the minute hand 13 of the clock mechanism 1. The sleeve 1'7is screw threaded on its exterior to receive the end turns of the coilspring 3 as shown. The other end of shaft 3 is fastened to shaft 11 ofcounting mechanism 2 through an insulated'coupling. The'couplingincludes an insulating sleeve 14 split longitudinally at one sidethereof and placed between the shaft 11 and the spring head 15 as shown.The spring head 15 contains a set screw 15a. to lock the head on shaft11 with insulated bushing 14 disposed therebetween. The spring head 15has a stud portion 15b projecting therefrom and threaded to receive theend turns of the coil spring 3. The hour hand 19 carried by tubularshaft 20 is permitted to run free of any connection with the shaft 3.

In operation the electrical circuit of the clock mechanism 1 isconnected to the cathode circuit of the radio transmitter as shown inFig. 1. As

long as the filaments of the tubes are operated the clock mechanism willalso operate. This is due to the arrangement of the electromagneticactuating mechanism of the clock shown at 24 and vgrounded at 22 to thecasing 1 and connected through binding post 23 with the externalfilament circuit of tube 25. We have selected the electric clockmechanism illustrated diagrammatically in Fig. l by reason of theability of this type of electric clock to operate from direct current aswell as alternating current. In lieu of the alternating current supplyillustrated for the electron tube apparatus there are many installationswhere only direct current is available, in which event the vacuum tubelife meter of our invention functions with the same precision as isobtainable with alternating current power supply. The electromagnet 24and associated armature illustrated constitutes the actuating mechanismof the rewinding element of the clock mechanism which periodicallystores energy into the clock spring to be expended in driving the clockmechanism and associated escapement as shown, for example, in the patentto Cooper 1,564,124, which issued December 1, 1925. The rewindingmechanism illustrated functions independently of the character of thepower supply. However in the embodiment of the invention illustrated inFig. 1, the power transformer 26 supplies the cathode heating potentialfrom an alternating current source connected to theprimary winding 26athrough circuit 26b. The secondary winding of transformer 26 isrepresented at 27 having a center tap 27a which is grounded to the panel10 and connected to ground indicated at 28. The

case of the counting mechanism 2 is often grounded by reason of aconnection established through the panel 10. It is therefore necessarythat the casing of the counting mechanism 2 be suspended in theinsulated yoke 4 and entirely insulated from the mechanism of thedriving means. This insulation is assured by reason of the insulatingsleeve 14 which wholly surrounds the counter shaft 11 and electricallyisolates the flexible shaft 3 from the counter mechanism. The fact thatthe clock mechanism 1 is wholly supported away from panel 10 preventsshort-circuiting with respect to the panel 10 and insures continuousoperation of theclock mechanism so long as power is supplied throughtransformer 26 to the cathode 25a of the electron tube 25. It will beseen that the drive mechanism 24 is connected across the cathode 25a andis actuated so long as cathode 25a is energized. By virtue of theisolation of the counter mechanism from the clock mechanism, nointerference to the operation of the circuits is offered as the metercontinues to measure the total time period over which vacuum tube 25operates. p

When the filaments are de-energized the clock is de-energlzed andtherefore will stop and no longer register on the dial 12 of countingmechanism 2. When a new tube is put in the radio transmitter a note ismade of the reading of dial 12. After this tube has burned out or hasbecome inoperative for other reasons another note is madeof the readingof dial 12. These two readings are subtracted and the total life of thetube is obtained. Subtracting any two successive clock mechanism 1 isgenerally one terminal of its electrical circuit, it is desirable toinsulate the case from ground. This is the reason for insulating part 5and bushing 14. A counter mechanism 2 may then be mounted very close tothe front panel of the radio transmitter which is generally grounded. Asuitable aperture 16 cut into the front of the panel will then permitobservation of the dial 12.

The readings taken on dial 12 may be recorded from time to time forchecking the operation or performance of particular electron tubes fordetermining the service received. The vacuum tube life meter isapplicable to electron tubes in amplification circuits of variousdescriptions such as telephone repeater circuits, radio transmitters,radio receivers, and all electron tube circuits, employing electrontubes of the more expensive types against which a careful check ofperformance must be maintained.

While we have described our invention in one of its preferredembodiments we desire that it be understood that modifications may bemade and that no limitations upon our invention are intended except asare imposed by the scope of the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States for governmental purposes, withoutthe payment of any royalty thereon.

What we claim as new and desire to secure by Letters Patent of theUnited States is as follows:

1. An electron tube life meter comprising a frame structure, an electricclock mounted on said frame structure, a flexible shaft extending fromone of the driven shafts of said electric clock, an insulated yokesupported on said frame structure, a mechanical counter suspended insaid insulated yoke and electrically insulated from said electric clock,and an insulated coupling between said flexible shaft and the drivingshaft of said mechanical counter for driving said mechanical counter,said insulated coupling electrically insulating said mechanical counterfrom said electric clock.

2. An electron tube life meter comprising a frame structure, an electricclock carried by said frame structure, an insulated yoke supported bysaid frame structure, a. mechanical counter insulatingly suspended bysaid yoke with the axis of the driving shaft of the mechanical counterextending in a. plane normal to the axis of the shaft of said electricclock, and a flexible connection extending between the driven shaft ofsaid electric clock and the driving shaft of said mechanical counter foreffecting the operation of said mechanical counter, and means forelectrically insulating said mechanical counter from said electricclock.

3. An electron tube life meter comprising a frame structure, an electricclock carried by said frame structure, an insulated yoke supported bysaid frame structure, a mechanical counter inof said mechanical counter,said coiled wire like member being turned to an angle of substantiallyQO" for operating said mechanical counter, said mechanical.counterhaving means supported by said frame structureand offset with'respect to the face of said electric clock, a mechanical countersupported by said insulated yoke 3 and electrically insulated from saidelectric clock, adriving member connected with said mechanical counter,and aflexible connection between the driven member of said electricclock and the driving member of said mechanical counter.

' LOUIS A. GEBHARD.

GEORGE E. JACOBSON.

